When designing wood frame structures, an architectural team must review fire ratings throughout the design process. Fire ratings measure how long a structure can withstand fire exposure. This is important to consider when constructing a safe, durable, and code-compliant building.
In this blog post, we will discuss the added value of the evaluation and approach that BKBM’s Structural Engineer Marie DesHarnais uses to assess the fire ratings of wood frame structures when working in partnership with architects through the design process.
Understanding Fire Ratings in Wood Frame Structures
Fire safety is a crucial consideration when designing and constructing wood frame structures. The ability of a building to withstand fire and prevent it from spreading for a length of time is measured by its Fire Rating, which is determined by a set of codes and regulations. Fire ratings can vary depending on the type of construction and the materials used.
The structure’s architect and structural engineer work in partnership and play a key role in evaluating the fire ratings of wood frame structures. They must thoroughly understand the codes and regulations and apply their knowledge to assess the structure's fire safety.
There are three main types of construction for wood frame structures: Type V, Type III, and to a lesser extent Type IV.
- Type V construction allows combustible materials, such as wood, to be used in exterior and interior walls.
- Type III construction requires noncombustible materials for exterior walls but allows flammable materials to be used in the interior. It also allows fire-retardant-treated wood to be used in exterior walls.
- Type IV construction is typically thought of as mass timber construction. It requires noncombustible or fire-retardant-treated wood for exterior walls and wood framing without concealed spaces for the interior.
The separation of room usage can also come with extra fire rating requirements, such as shafts, trash rooms, and parking.
Structural engineers must evaluate the materials and framing methods used in the building and verify they meet the load-carrying requirements while maintaining fire ratings for the chosen construction type. When engaged early in the concept phase of a project, structural engineers can assist in vetting out cost-effective construction types that meet the project's target use, load, fire ratings, and aesthetics. Structural engineers may also recommend modifications to framing during design to improve cost, constructability, or durability for fire-rated construction.
Fire ratings in wood construction often come down to the detailing, where the integrity of fire ratings can be made or broken through the connections between rated elements. Structural engineers must design connections between elements to transfer forces, maintain fire ratings, and be constructible.
Approach of BKBM’s Structural Engineers in Detailing with Fire Ratings
BKBM’s multi-family housing structural engineers, like Marie DesHarnais, PE have great experience working with fire ratings for wood frame structures. Our team of 14 structural professionals understands and can readily work with the project's fire protection objectives, including:
- the necessary fire-resistance rating of structural elements,
- fire barrier and partition placements,
- typical connection detailing for rated assemblies based on our experience with what can be built efficiently and effectively, and
- innovative detailing for unique framing configurations
Our team collaborates with our architects and other project team members from the start of the project to proactively identify potential issues and devise innovative solutions to meet fire ratings while maintaining the structural integrity of the building.
Furthermore, we collaborate with contractors to adapt our framing design for constructability and cost-effectiveness. With thorough detailing, we provide contractors the direction to build structural connections as we design and accurately estimate project costs. We know material and labor costs constantly change, and new technologies are emerging to improve fire ratings, constructability, and sustainability. Working with contractors to leverage their expertise in current costs and construction practices helps us improve our design to work with the project's time, team, and location, while building on our past experiences.
By taking a comprehensive and collaborative approach to evaluating fire ratings in wood frame structures, structural engineers play a crucial role in ensuring the safety and integrity of the building for all its occupants.
Experienced Collaboration for Efficient Design
The presence of a structural engineer knowledgeable in fire ratings of a wood frame structure in design is invaluable. This partnership empowers the design architect to focus on their key strengths of molding the built space to meet the client’s needs while having the assurance of an expert collaborator handling the structural components of the project. This enhances efficiency, optimizes resource utilization, and assures a high confidence level in the overall design. By joining forces with an experienced structural engineer, the design architect can create an aesthetically pleasing and functional project that adheres to the required fire safety codes and regulations.
Structural Engineering Expertise and Reliability for Multi-Family Housing Projects
Marie DesHarnais is a Minnesota registered engineer with nearly ten years of experience designing wood-frame multi-family housing complexes for BKBM. She has a reputation as a thorough and process-driven individual who is unafraid of the challenges associated with delivering an optimized solution to any given problem. Her expertise has been developed as she has designed structures supporting up to 3,000 units in her time with BKBM. Her wealth of knowledge and drive to deliver make her an ideal partner for any wood multi-family housing project, and she stands ready to offer her services.